According to image compression methods including Moving Picture Experts Group-1 (MPEG-1), MPEG-2, MPEG-4 H.264/MPEG-4 Advanced Video Coding (AVD) or the like, in order to encode an image, a picture is divided into image processing units, i.e., macroblocks. Each macroblock is then encoded by using inter-prediction or intra-prediction.
However, when these related art image compression methods are used, blocking artifacts are generated in the decoded image. The image compression methods involve performing a discrete-cosine-transformation and a quantization each sub-block (e.g., a 4×4 block) included in a macroblock. Since the sub-blocks are independently discrete-cosine-transformed and quantized without consideration of adjacent blocks, an image loss occurs in the macroblock, and thus, blocking artifacts that cause noticeable edges between macroblocks are generated in the decoded image. Accordingly, a deblocking filter is used to improve the visual quality of the decoded image by smoothing noticeable edges that occurred in a block-based coding operation.